1. Field of the Invention
The present invention relates to a latch circuit, a flip-flop circuit including the latch circuit, and a semiconductor device including the flip-flop circuit.
2. Description of the Related Art
A semiconductor device such as a large-scale integrated circuit (LSI) is constituted by a logical gate that is a circuit processing a digital logical value and a circuit which temporarily holds the digital logical value. Typical examples of the logical gate include an inverter, an AND, an OR, a NOR, and a NAND. Further, typical examples of the circuit which temporarily holds a digital logical value include a latch circuit and a flip-flop circuit.
In recent years, a semiconductor device which consumes less power while keeping the processing speed at the same level as conventional semiconductor devices has been required. There is a known method in which power consumption is reduced by stopping supplying power to a circuit which is not driven or the whole semiconductor device.
However, by this method, data which has been held in a volatile latch circuit or flip-flop circuit is erased even when supply of power is restarted after power shutdown. To solve the problem, there is a backup method in which in order to hold data reliably while power is not supplied, data is written to a nonvolatile memory element that operates at low speed immediately before supplying power is stopped, and a latch circuit, a flip-flop circuit, or the like is driven while power is supplied to the semiconductor device.
Further, a latch circuit which is nonvolatilized (nonvolatile latch circuit) including a ferroelectric capacitor has been proposed in order to hold data by a latch circuit even in a state where power is not supplied (see Patent Document 1).